The present invention relates to a car audio device such as a car stereo device, a car radio or the like, and, more particularly, to a car audio device in a system (a so-called detachable system) in which a body part and an operational part are detachable from each other.
Each of detachable car audio devices has a configuration which is divided into two functional parts so that one of the functional parts can be fixed to the inside of a car, specifically, to the dashboard of a cockpit, and the other can be freely attached to and detached from the body unit. The fixed part is called a body part, and the detachable part is called a detachable grill (corresponding to an operational part). The body part accommodates, for example, a mechanism part such as the mechanism part of a cassette tape recorder, the mechanism part of a CD (compact disk) player and the system controller (microprocessor) of the audio device of the present invention or the like. The detachable grill has an indicator panel serving as a base onto which central functional parts such as input keys, input controllers, various displays, a display driver remote control receivers and the like are mounted or in which these parts are received. The body part and the detachable part are detachably combined by a mechanically using a lock mechanism which can be released. They are also electrically detachably connected to each other through contact terminals which are electrically connected to each other and which are provided at corresponding positions. A plurality of contact terminals are provided in correspondence with the number of signals transmitted between the two parts and include a terminal for a power line. In this way, the body part and the detachable grill can be separated from each other, and the audio device does not function as an audio device in a state wherein the detachable grill is detached from the body part. It is therefore possible to prevent robbery of the audio device by detaching and taking a way the detachable grill when the driver gets off a car.
However, the above-described conventional car audio devices has the problem that communication between the display driver and the key input controller on the side of the detachable grill and the system controller on the side of the body part is performed by a system bus, and the problem that the same system bus is also used as a control bus for a CD player in the body part. That is, the first problem causes the complication of connective relation between the detachable grill and the body unit owing to the presence of many signal lines in the system bus and thus causes the complication of connection between the contact terminals. The second problem causes the noise produced between the contact terminals when the detachable grill is attached and detached to be mixed in the audio device through the system bus, resulting in the occurrence of malfunction.